Gaseous fuel vehicles have widely been developed in recent years to reduce impacts on the environment. The gaseous fuel vehicle is provided with a gaseous fuel tank in the rear of the vehicle. Various frame structures for holding a gaseous fuel tank have been developed. In Japanese Patent Laid-Open Publication No. 2000-219050, for example, a vehicle frame structure is proposed which is configured to hold two gaseous fuel tanks which are oriented transversely and arranged one behind the other in parallel below vehicle rear cushions.
In Japanese Patent Laid-Open Publication No. 2003-63457, a vehicle frame structure is proposed in which a gaseous fuel tank is mounted on a support frame, and the support frame is mounted to right and left rear frame members, whereby the gaseous fuel tank is mounted to the rear of a vehicle.
The rear structure of the gaseous fuel vehicle disclosed in the 2003-63457 publication will be described below with reference to FIG. 24 hereof.
A vehicle rear structure 800 shown in FIG. 24 includes a support frame 801 on which front and rear two gaseous fuel tanks 802, 803 are mounted transversely. The support frame 801 is mounted to left and right rear frame members 804, 805. The front and rear gaseous fuel tanks 802, 803 are accommodated in a space 810 between the left and right rear frame members 804, 805 and the support frame 801. Thus, the front and rear gaseous fuel tanks 802, 803 are protected by the left and right rear frame members 804, 805 and the support frame 801.
Front ends 804a, 805a of the left and right rear frame members 804, 805 are offset above left and right side sills 806, 807 in order to secure the space 810. Therefore, it is necessary to connect the front ends 804a, 805a of the left and right rear frame members 804, 805 to the rear ends of the left and right side sills 806, 807 by a connector 808.
The connector 808 includes a left extension 811 extending rearward from the rear end of the left side sill 806. A left bracket 813 is attached to the left extension 811. The connector 808 also includes a right extension 812 extending rearward from the rear end of the right side sill 807. A right bracket 814 is attached to the right extension 812.
It is necessary to provide the connector 808 with strength so that when a load is applied to a bumper beam 809 provided at the rear ends of the left and right rear frame members 804, 805 as shown by an arrow, the applied load can be transmitted to the left and right side sills 806, 807.
In order to ensure the strength of the connector 808, it is required to increase the rigidity of the left and right extensions 811, 812 as well as reinforcing the left and right extensions 811, 812 by the left and right brackets 813, 814. This causes a complicated configuration of the rear structure 800 of the gaseous fuel vehicle, and can prevent a weight reduction of the rear structure 800 of the gaseous fuel vehicle.
Also, since the left and right rear frame members 804, 805 are arranged above the front and rear gaseous fuel tanks 802, 803, it is necessary to offset the front ends 804a, 805a of the left and right rear frame members 804, 805 above the left and right side sills 806, 807. This arrangement makes it difficult to reduce the height of the front ends 804a, 805a of the left and right rear frame members 804, 805, preventing a low floor in a passenger compartment.
For these reasons, there is a desire for an art which allows for simplify-cation and weight reduction of a rear structure, and also allows for a low floor in a passenger compartment.
A support structure for the front and rear gaseous fuel tanks 802, 803 shown in FIG. 24 will be described with reference to FIG. 25.
Referring to FIG. 25, a gaseous fuel tank support structure 820 includes the support frame 801 for holding the front and rear gaseous fuel tanks 802, 803.
A pair of front holding bands 822, 822 are fastened around the front gaseous fuel tank 802 and attached to the support frame 801 by a plurality of bolts 826 via front mounting brackets 823, 823 and rear mounting brackets 824, 824 for the front holding bands 822, 822. That is, the front gaseous fuel tank 802 is fixed to the support frame 801 with the front holding bands 822, 822.
As in the front gaseous fuel tank 802, a pair of rear holding bands 832, 832 are fastened around the rear gaseous fuel tank 803 and attached to the support frame 801 by a plurality of bolts 826 via front mounting brackets 833, 833 and rear mounting brackets 834, 834 for the rear holding bands 832, 832. That is, the rear gaseous fuel tank 803 is fixed to the support frame 801 with the rear holding bands 832, 832.
The center of gravity of the rear gaseous fuel tank 803 is located at the center height G2. The difference in height between the center of gravity G2 and the support frame 801 is L.
When the vehicle is running on a bad road, longitudinally moving forces act on the rear gaseous fuel tank 803, and horizontal forces act on the center of gravity G2 of the rear gaseous fuel tank 803. As a result, moments (overturning moments) of (horizontal force)×(height difference L) act on the front mounting brackets 833 and the rear mounting brackets 834.
To withstand the moments, it is necessary to increase the strength of the front and rear mounting brackets 833, 834 and the bolts 826. According to the increased strength of those components, it is necessary to increase the thickness of the rear holding bands 832, 832 to increase the strength.
The same is true for the front gaseous fuel tank 802, and is not described redundantly.
For these reasons, there is a desire for an art of supporting a gaseous fuel tank which allows for reduction in strength of mounting brackets and holding bands.